Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!ucbvax!decwrl!megatest!djones
From: djones@megatest.UUCP (Dave Jones)
Newsgroups: comp.software-eng
Subject: Re: Recursive #includes
Message-ID: <2532@goofy.megatest.UUCP>
Date: 27 Feb 89 23:19:43 GMT
References: <570@marob.MASA.COM>
Organization: Megatest Corporation, San Jose, Ca
Lines: 38

From article <570@marob.MASA.COM), by samperi@marob.MASA.COM (Dominick Samperi):
) Are recursive #includes hazardous to your software's health? 
) 
) I'm working on a system where each header file has the form:
) 
) <contents of foo.h):
) 
) #ifndef H_FOO
) #define H_FOO
) 
) defines, declarations, etc.
) 
) #endif
) 

It is very hazardous to your health.  If you write recursively
nested include-files, you can work yourself into all sorts of 
quandries if things get a little messed up. (I speak from experience.)

The reason for the #ifndef is not for recursively defined headers.
(Use undeclared struct-this and struct-that for forward references.)
It is to let you include that include-file without worrying about
whether some other include-file has already included it. (There are
some who reject includes in includes, for this very reason, but 
that's a different holy war.)

So.... do this instead:

 
 #ifndef H_FOO

  defines, declarations, etc.

 #define H_FOO 
 #endif
 

This allows you to include an include-file twice, but not recursively.